1. Field of the Invention
The present invention relates generally to a power controller for a vehicle. More particularly, the invention relates to a control system for an automotive power source system suitable for controlling an automotive power source having a higher voltage and higher capacity battery than the conventional 14V system, such as 42V system.
2. Description of the Related Art
In recent years, to accommodate the increasing number of electrically actuated on-vehicle devices, such as electrically driven power steering, electrically actuated air conditioner and so forth, and the increasing capacity thereof, it has been proposed to provide a 42V automotive power supply in addition to the convention 14 power supply. In the 42V power supply, since the voltage is three times higher than that of the 14V system, the current can be reduced by one third, reducing power loss and saving on the weight of a harness. Also, adaptation for a large capacity load is facilitated, and the capacity of the battery is larger than that of the conventional battery, and a nickel hydride battery, lithium ion battery and so forth can be applied in place of the conventional lead acid battery for the future. Recently, it has been proposed to provide a system having both a main battery of a 42V system and an auxiliary battery of a 14V system, with both batteries connected through a DC/DC converter for controlling charging from the main battery to the auxiliary battery.
However, in the recently proposed system, the following problem can be encountered. Namely, by utilizing the large capacity of the battery of a 42V system, it is possible to operate an electrical load, such as an electrically actuated air conditioner, even while the engine is not driven. However, when the remaining capacity of the main battery becomes small, it is impossible to start the engine.
Also, for example, when the lamps are connected to the 14V system, it becomes necessary to turn the lamps ON even when the key switched remains OFF. However, when the capacity of the auxiliary battery is small, remaining capacity is instantly lowered to the lower remaining capacity of the main battery when the lamps are kept ON.